Poly-2-pyrrolidone (also known as nylon-4) is a polymeric carbonamide of relatively high molecular weight which has recurring amide groups separated by a trimethylene radical as an integral part of the main polymer chain. The polymer is capable of being formed into filaments having substantial orientation along the filamentary axis, high tensile strength, and other properties suitable for mixing into textiles. The polymer can be made into filaments, shaped articles and films by melt spinning, molding and extruding.
Usually, the polymerization of 2-pyrrolidone to poly-2-pyrrolidone involves adding potassium hydroxide to 2-pyrrolidone, distilling off the water of reaction, adding carbon dioxide, charging the reaction mixture to a container or conveyor and reacting at about 50.degree. C. for several hours. The polymer is then recovered by cutting the solid product into manageable pieces and extracting the alkaline polymerization catalyst and excess monomer with water (U.S. Pat. No. 3,721,652). Since polymerization usually proceeds to about 50-70% conversion of monomer, or less, there is appreciable monomer to be recovered from the dilute aqueous washes and the catalyst may be completely lost.
U.S. Pat. No. 2,739,959 discloses the polymerization of 2-pyrrolidone in a non-solvent for the monomer to recover a powdery product from the agitated reaction mixture. U.S. Pat. No. 3,213,066 discloses the carrying out of the polymerization of 2-pyrrolidone in suspension or in bulk in a ball mill to recover a finely divided solid product. In U.S. Pat. No. 3,681,293 and U.S. Pat. No. 3,804,813 the partially solidified reaction mixture is pelletized and the pellets are cured to achieve normal conversion. Each of these processes has the problem of monomer recovery from aqueous washes and catalyst loss.